1. Field of the Invention
The present invention relates to a quantum dot electroluminescence device and a method of fabricating the same. The present invention also relates to a quantum dot electroluminescence device using a quantum dot thin film in which a plurality of quantum dots are arranged in two-dimensions, and a method of fabricating the same.
2. Description of the Related Art
A conventional organic light emitting device (OLED) generally has a multilayered thin film structure composed of a low-molecular organic material. While the conventional OLED has advantages of various materials selectable for a thin film, easy formation of a high purity thin film, and a high luminescence function, it has problems with oxidation or crystallization as a result of reactions with foreign harmful materials. Further, since it is formed at a predetermined position using a vacuum evaporation, it has a problem of requiring a complicated and high-cost film formation process.
Recently, studies of luminescence devices using the luminescence characteristics of quantum dots were conducted. Normally, in the quantum dot electroluminescence device, a low-molecular weight organic material, which has been used in OLEDs such as Alq3, is formed on a luminescence layer using vacuum evaporation. The low molecular weight organic material functions as an electron transfer layer. Since the thin film composed of the organic material reacts with harmful materials such as oxygen or moisture, originally amorphous thin film may become recrystallized or oxidized. As a result, dark spots are often generated on the thin film with a loss of the display function. The luminescence device also loses efficiency and deteriorates as a result of this undesirable reaction with oxygen and moisture.
In order to prevent such deterioration, and maintain the display function, it is desirable to protect the organic thin film from harmful materials, and a plurality of shield layers have been required to seal the organic thin film. Thus, additional thin film formation processes are used. The shield structure uses vacuum evaporation requiring expensive vacuum evaporation equipment, skillful technology, and a plurality of processing steps, and therefore increases the manufacturing costs of electroluminescence devices.
There is also a quantum dot electroluminescence device that comprises the electron transfer layer composed of n-GaN and a hole transfer layer which is used along with the electron transfer layer and is composed of p-GaN. However, since the n-GaN material layer formed on the quantum dot luminescence layer is formed using vacuum evaporation, complicated manufacturing processes and large-sized manufacturing systems are used. Thus the problem of high-expensive manufacturing costs still remains. Therefore, limitations of technology and economical problems still exist in employing the technology for large-area luminescence devices, and the quantum dot thin film may be damaged during the evaporation process maintained at a temperature of about 300° C., and particularly, there occurs a problem that a luminescence efficiency is low.
FIG. 1 is a photograph illustrating a section of a conventional quantum dot thin film examined using a transmission electron microscopes (TEM), and FIG. 2 is a sectional view illustrating the alignment state of quantum dots in the conventional quantum dot thin film of FIG. 1. As shown in the drawings, when an interface 51 of a quantum dot luminescence layer 50 is examined under a microscope, the interface 51 does not have an even surface and is formed rough due to limitations in the manufacturing processes. More specifically, the quantum dot luminescence layer 50 composed of quantum dots 50a cannot be formed on the entire surface of the substrate 10 with a uniform thickness, but forms a monolayer or multilayer locally depending upon their positions. This disposition produces voids where the quantum dots do not partially exist. A hole transfer layer 30 and an electron transfer layer 70 disposed on and below the quantum dot luminescence layer 50 contact each other directly at the voids, and generate a micro-short. This combination of holes and electrons injected through an anode electrode 20 and a cathode electrode (not shown) are recombined at the voids so as to locally generate large current. Thus, the generation of a useless leakage current, which does not pass through the quantum dots 50a and which does not contribute to luminescence operation, causes a loss of power consumption., The operation efficiency of the luminescence device is deteriorated, and neighboring thin film structures are deteriorated due to the electric heating effect.